Detection of anomalous circuit characteristics is the domain of both quality control as well as trusted computing. This is a trend in technology to ensure that devices being used in an application are the intended devices. In addition detection of anomalous circuit characteristics can be accomplished using different modalities, and several of these modalities have not been described previously for this purpose.
Miniaturization and Integration are continuing trends in technology that decrease the size of a device while maintaining its operational characteristics. When applied to electronic diagnostic equipment, this can allow for the more convenient use of that equipment, the more efficient use of space in space constrained environments, and retrofitting.
The components used in circuit boards are especially susceptible to counterfeiting and tampering. Counterfeit electronic and electrical components have found their way into the supply chain in increasing numbers. Counterfeiting occurs at the die, part, device, board and fully assembled product level. With the increasing complexity of counterfeiting and circuit tampering new detection and mitigation options have been needed for some time.
Prior to the conception and design of the instant invention, efforts have been made to inspect and screen counterfeits. However, a solution has not existed to detect if a counterfeit component was introduced onto a circuit board during rework or to have an on-board mechanism that could detect the installation of a counterfeit whether that counterfeit was introduced during the manufacturing process or at a later stage.
Prior to the instant invention all of the techniques are either superficial or extremely expensive and none of them are installed in-situ with the circuitry that needs to be monitored. Of superficial techniques, the simplest is visual inspection, but as counterfeits have become increasing sophisticated these techniques have become less reliable. In contrast, reliable techniques that are in existence are expensive or are destructive in nature.
One of the methods of choice for tampering with the integrated circuit at a die level, is the Focused Ion Beam (FIB). An astute reverse engineer can use FIBs to create, modify, or remove connections within an integrated computational or data storage asset to affect its operation. Whether these changes are malicious or simply part of a manufacturer's approach to cost savings, capabilities of detecting any modifications or changes to parts are of the utmost importance.
As noted, FIBs are a very effective tool to modify integrated circuits. The ability of these systems to ablate dielectric, metal, and substrates by bombarding the surface with Ge+ ions can cut electrical connections, create additional unauthorized features, and implant ions to create gates and transistors. FIBs can also be used in conjunction with gas sources to deposit layers of metal or other dielectrics using a variation on ion induced chemical vapor deposition. This gives a talented engineer the ability to deconstruct a non-volatile computational die (such as one found in a CPLD [Complex Programmable Logic Device] or FPGA) and adjust the bit patterns or hard-wired circuit elements. However, there are some tell-tale signs of using FIBs to modify a semiconductor die.
FIBs are inherently destructive as they irrevocably affect the crystalline structure of the die on which they are used, and result in an amorphous structure when used for deeper milling, especially with silicon. 1) FIBs inevitably leave a Ga+ doping residue embedded in the substrate. 2) For buried devices or lines, one must first mill, then modify the device, then refill the dielectric. This changes propagation, permittivity, and group delay of internal signals as well as radiated emissions.
From a computational point of view, these modifications may not necessarily affect the noticeable digital operation of the device in question, though they certainly could introduce additional delays, and affect timing constraints. From the point of view of electromagnetic emissions, however, these introduced defects are precisely the sort of things that affect trace (and consequently radiator) length, engineered electromagnetic interference (EMI) protection, grounding and terminating resistors, carefully controlled transistor junction length and transconductance, specific dielectric permittivity, isolation of intentionally suppressed or inherent low-level electromagnetic emissions, etc. In fact, even effects introduced by inherent process variations are so pronounced within modern technology nodes that the modeling and iterative analysis to control these effects are now considered the most difficult element of the design process. For example, even modest levels of increased capacitance (femtofarad levels) generated from line width variations during manufacturing are capable of increasing crosstalk, ground bounce and delay at appreciable levels in modern circuits. In the spectral domain, this can drastically affect the strength, frequency, phase, harmonic content, and bandwidth of an emission. In the time and time-frequency domain, the phenomenology can be even more distinctive.
Thus, there is a need for a device capable of detecting anomalies due to counterfeiting, aging, discrete events that may degrade a component or tampering at the part and a die level of the integrated circuit or other complex semiconductor based devices and assemblies.